#include<iostream>
using namespace std;
int n,m,i,j;
int main()
{
    int hx,hy,a[21][21],f[21][21];
    cin>>n>>m>>hx>>hy;
    for(i=1;i<=n;i++) f[i][1]=1;
    for(i=1;i<=m;i++) f[1][i]=1;
    f[hx-2][hy+1]=f[hx-1][hy+2]=f[hx+1][hy+2]=f[hx+2][hy+1]=f[hx+2][hy-1]=f[hx+1][hy-2]=f[hx-1][hy-2]=f[hx-2][hy-1]=f[hx][hy]=1;
    for(i=2;i<=n;i++)
        for(j=2;j<=m;j++)
            if(f[i][j]!=0) a[i][j]=a[i-1][j]+a[i][j-1];
    cout<<a[n][m];
    return 0;
}